Screw holding screw driver



March 27, 1956 J. M. NEIL 2,739,629

SCREW HOLDING SCREW DRIVER Filed March 16, 1953 2 Sheets-Shem 1 FlGURE I 24 I I V I l 23 I ll/, \w] H FIGURE 2 I l:24 Z3 11 FIGURE 5 FlGURE 4 JAMES M. NEIL INVENTOR.

A7 TOIZNEV March 1956 J. M. NEIL 2,739,629

SCREW HOLDING SCREW DRIVER Filed March 16, 1953 2 Sheets-Sheet 2 I s F Flame: 5 Kl D E i M FaeueE 8 A Ei FIGURE 6 FIGURE 7 Y E G M JAMES M.NE|L

IN V EN TOR.

United States Patent SCREW HOLDING SCREW DRIVER James M. Neil, Oakland, Calif. Application March 16, 1953, Serial No. 342,484

2 Claims. (Cl. 145-50) This invention relates to screw drivers of the screwholding type and particularly those employing a bifurcated bit with a holding member rotatable therein. Such a screw driver is shown in my copending application Serial Number 277,826, filed March 21, 1952.

The object of the invention is to construct the holding member so as to increase its effective holding power and at the same time decrease its destructive effect on the screw slot. This can be more readily explained by reference to the drawings, in which:

Figure 1 is an elevation of the screw driver disclosed in detail in my before-mentioned application.

Figure 2 is a horizontal section taken as indicated by line 2-2 in Figure 1.

Figure 3 is a view similar to Figure 2 showing my improved holding member.

Figure 4 is an elevation of the bit and holding member shown in Figure 3.

Figure 5 is a construction drawing showing the holding member in end elevation.

Figures 6 and 7 show the holding member functioning in slots of different width.

Figure 8 is a diagram to illustrate the derivation of the equation of the curve.

Figure 1 shows the screw driver with a screw 10 attached thereto. This was effected by inserting the bit 11 in the slot of the screw and pushing the button 12, which caused the holding member 13 to be rotated by a spring means within the handle 14 to grip the screw as shown in Figure 2.

While this is an effective method of holding the screw, its disadvantage is that the corners 21, 22, of the holding member 13 dig into the walls 23, 24, of the slot in the screw 10. Users object to this marring and mutilating of the slot.

In accordance with my invention the holding member 30 is provided with rounded corners 31, 32, as shown in Figures 3 and 4. This prevents mutilation of the slot, but to avoid loss in holding power 1 form the corners in such a way as to cause the rounded surfaces 31, 32, to jam and bind against the walls 23, 24. However, this raises a problem, namely, that the holding member must adapt itself to slots of different width, so that a haphazard or superficial rounding of the corners of the holding member will not provide the complete answer.

After investigating the adaptability of various curves, such as spirals, I found that the arc of a circle eccentric to the center of rotation of the holding member gives the desired result.

Referring now to the construction diagram in Figure 5, it was assumed that the width AB was one-third the overall length. It was also assumed the holding member was capable of ninety degrees rotation on its axis or center C.

The following requirements were laid down:

1. The holding member must fit slots varying in width from a minimum equal to the width of the member to a maximum equal to the length. See Figures 5 to 7.

2. To get maximum jamming action the points of con- 2 tact between the holding member and the slot walls must be kept as close to the horizontal axis as possible.

3. Every point of contact must be a true kinematic point of contact, that is, it must lie on the line of centers of the curve and the wall.

To satisfy the first two requirements, the radius of the arc is made equal to the width AB, and since the length was predetermined, the center of the arc is located at E, so that FE equals AB, and angle ECD is a right angle. Point B will travel in arc EKD as the member rotates through the prescribed ninety degrees.

Finally, as illustrated by Figures 5 to 7, the third requirement is met. In the first position (Figure 5) the point of contact D is on the line of centers EM, B being the center of curvature of the arc PD, and the center of curvature of the slot wall SS, being M, which is at infinity. In the wider slot shown in Figure 6, the point of contact P is on the line of centers EM. And, in the maximum width slot (Figure 7), which is equal to the length of the member, the point of contact R is on the line of centers EM.

Because I do not wish to be limited to the particular configuration just described, I will show the derivation of the equation of the curve FD with the origin at the center of rotation C.

GH is the arc of a circle whose center is at O and whose radius is r. Q is any point on the curve and its coordinates are (x, y). Thus is the equation of the curve GH.

To efiect transformation of coordinates by translation of axes:

Locate the new origin at O' and draw axes XX' and YY parallel to axes XX and YY, respectively. Extend QL to intersect the XX' axis at T. The coordinates of point Q in the new system are (x', y).

The rule for transformation of coordinates is: If x and y are the coordinates of any point before translation to a new origin (h, k) and x and y the coordinates of the same point after translation then Draw the line 00' and represent its length by m and its location by 6. Now

k=m cos 0 k=m sin 6 Substituting these values in ,(2) and (3) y=y'+m sin 0 Substituting these values in (1) (x=m cos 0) +(y+m sin 0) =r It is customary to drop the primes when the transformation is completed so the equation of the curve GH in the new system of coordinates whose origin is at the center of rotation instead of the center of curvature is I claim:

1. In a screw driver, a bifurcated bit, an element disposed in the center of said bit, said bit and said element being adapted to rotate relative to each other to grip a screw, the axes of said bit and said element coinciding, said element having surfaces for engaging the walls of the slot in a screw, the profile of each surface being a curve whose origin is at the center of rotation of said 3 element, said curve being defined by the equation: (x-i-m cos 0} +(y+m sin 6) =r wherefl is the angular disposition of a line joining the center of curvature of said curve with the center of rotation of said element, m the length of said line, andr the radius of curvature, and where the value of m is other than zero.

2. In a screw driver, a bit having an axis about which said bit is turned to rotate a screw, an element adapted to cooperate with said bit to hold the screw, a crosssection of the portion of said element that engages the screw being greater in length than in width, said element and said bit being-relatively rotatable to operate in screw slots having a range in width from the width of said cross-section to the length of said cross-section, the outline of said cross-section consisting of two straight lines and two curves joining adjacent ends of said straight lines, there being two points of contact between said cross-section of said element and the walls of the slot in a screw, one of said points of contact being on one of said curves, the other of said points being on the other of said curves, all points of contact with the walls of screw slots in said range being on said curves, a different pair of points for each width of slot.

References Cited in the file of this patent UNITED STATES PATENTS 

